BORDETELLA BRONCHISEPTICA
LEVELS: Rarely occurs: Requires significant failure at one or more control points for transmission to humans; Highly unlikely: No evidence of non-foodborne zoonotic transmission; Not applicable: Agent is ubiquitous on all or most US farms; Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s); Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals; Negligible: Little or no market disruption when disease occurs on one or more farms; Moderate risk: Evidence of development of clinically important resistance to antibacterial or antiviral treatments, or that development of such resistance is likely to occur over time; High risk: Antibacterial or antiviral treatments commonly used on affected groups, or for prophylaxis; Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations; Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent; Not feasible: Eradication extremely unlikely
OVERVIEW
Bordetella bronchiseptica is an aerobic, motile, gram-negative coccobacillus that plays multiple roles in swine respiratory disease worldwide. It is the primary etiologic agent of nonprogressive atrophic rhinitis (NPAR), a mild-to-moderately severe, reversible condition affecting the nasal turbinates. More importantly, nasal colonization by B. bronchiseptica promotes colonization by toxigenic strains of Pasteurella multocida, leading to severe progressive atrophic rhinitis (PAR). In young pigs, B. bronchiseptica causes necrohemorrhagic bronchopneumonia, and in older pigs, it contributes to the porcine respiratory disease complex (PRDC) as an opportunistic pathogen. The organism also enhances respiratory colonization by Streptococcus suis and Glaesserella parasuis, and interacts synergistically with PRRSV and influenza A virus to increase respiratory disease severity. B. bronchiseptica is highly prevalent among swine, frequently isolated from both pneumonic and apparently healthy pigs. Transmission occurs primarily by aerosol droplets and is facilitated by close contact. Many litters are colonized before weaning from nursing sows. The organism persists in the nasal cavity for months, possibly indefinitely, with carriers serving as reservoirs for ongoing transmission. Key virulence factors include dermonecrotic toxin (DNT) essential for turbinate atrophy and pneumonia, filamentous hemagglutinin (FHA) for adhesion, adenylate cyclase toxin (ACT), tracheal cytotoxin (TCT), and a type III secretion system. Vaccination reduces disease severity but does not eliminate colonization or the carrier state.
FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Rarely occurs: Requires significant failure at one or more control points for transmission to humans
Human illness from B. bronchiseptica is rare, and no foodborne transmission has been documented. The chapter states: "Human illness resulting from B. bronchiseptica infection is rare but on the rise." Cases involve direct respiratory transmission rather than foodborne routes: "A variety of clinical presentations have been documented, including tracheobronchitis, whooping cough, pneumonia, sinusitis, septicemia, meningitis, and peritonitis." The at-risk populations are "infants and immunocompromised individuals with exposure to carrier animals." There is no evidence that consumption of pork products poses any risk of B. bronchiseptica transmission to humans.
NON-FOODBORNE ZOONOTIC TRANSMISSION POTENTIAL
Level: Highly unlikely: No evidence of non-foodborne zoonotic transmission
Human infections occur but are uncommon and typically associated with pet exposure rather than swine: "In many cases, exposure to domesticated pets, particularly dogs, cats, and rabbits, is the presumed source of infection. No human cases related to transmission from swine have been reported." However, the chapter notes: "Whether swine can act as a reservoir and transmit B. bronchiseptica to humans or vice versa is plausible but currently unknown." One swine-origin isolate has been found among human-associated B. bronchiseptica strains, but direct transmission from pigs to humans remains undocumented. The broad host range of B. bronchiseptica creates theoretical risk, but swine-specific transmission to humans has not been established.
EFFECTIVENESS OF ON-FARM BIOSECURITY IN PREVENTING FARM-TO-FARM TRANSMISSION
Level: Not applicable: Agent is ubiquitous on all or most US farms
B. bronchiseptica can spread despite standard biosecurity measures through multiple routes: (1) Aerosol transmission: "Transmission of B. bronchiseptica occurs primarily by aerosol droplets"; "airborne transmission over short distances, including within a barn or production unit, is probable"; (2) Environmental persistence: "The bacterium remains viable for up to 45 days in soil" and "at least several weeks in lake water"; "The half-life of aerosolized organisms at ambient temperature and approximately 75% relative humidity is 1–2 hours"; (3) Wildlife reservoirs: "B. bronchiseptica has been isolated from rodents, birds, raccoons, opossums, and other animals trapped in close proximity to swine"; "cross-species transmission to pigs following exposure to infected wild animals or domesticated pets...may occur"; (4) Carrier introduction: "Newly purchased breeding stock may be a source of infection"; (5) Ubiquitous prevalence: The organism is "highly prevalent among swine." While disinfection is effective ("sensitive to several chemical disinfectants suitable for farm use"), the combination of aerosol spread, environmental survival, and wildlife reservoirs means some biosecurity bypass occurs.
DIFFICULTY OF DETECTING AND CONFIRMING INFECTION
Level: Easy: Distinct clinical signs and/or existing test(s) available at local/regional laboratory(s)
Multiple well-validated diagnostic methods are available: (1) Culture: "B. bronchiseptica grows readily on blood agar" and on selective media; "Convex colonies, roughly 1–2 mm in diameter, develop hemolytic on blood agar and develop after 36–48 hours"; (2) Biochemical identification: "positive for oxidase, catalase, urease, and citrate"; (3) MALDI-TOF MS: "widely used in diagnostic laboratories" and "capable of identifying Bordetella to the species level"; (4) PCR: "sensitive and specific for B. bronchiseptica when tested with bacterial genera and species commonly found in the swine respiratory tract"; (5) Serology: ELISA available for serum or nasal secretions; "may be useful for monitoring the status of a herd"; (6) Molecular typing: MLST, PFGE, and genome sequencing available for strain characterization. The main diagnostic challenge is determining B. bronchiseptica's contribution to disease in mixed infections where it "most commonly occurs...together with one or more other respiratory disease agents."
FINANCIAL IMPACT ON FARM'S COST OF PRODUCTION
Level: Substantial: Unsustainable acute or chronic losses related to severe clinical signs in a high prevalence of animals
B. bronchiseptica causes substantial direct and indirect economic losses: (1) Direct disease losses: Primary bronchopneumonia in suckling pigs can cause "dyspnea, lethargy, and sometimes death"; NPAR causes "mild-to-moderately severe" turbinate damage; (2) PAR facilitation: "nasal colonization by B. bronchiseptica promotes colonization by toxigenic strains of Pasteurella multocida, which leads to severe, progressive atrophic rhinitis"—PAR causes snout deformity, reduced growth, and production losses; (3) PRDC contribution: B. bronchiseptica acts as "an opportunistic pathogen contributing to the porcine respiratory disease complex"; (4) Enhanced secondary infections: "B. bronchiseptica can also enhance respiratory colonization of Streptococcus suis and Glaesserella parasuis, promote disease caused by S. suis" with "increased mortality"; (5) Viral synergies: Coinfection with IAV or PRCV leads to "increased severity of pneumonia with an earlier onset and longer resolution"; PRRSV coinfection leads to increased pulmonary infection with P. multocida; (6) Ubiquitous presence: High prevalence means ongoing production impact across the industry.
EFFECT ON DOMESTIC OR EXPORT MARKETS
Level: Negligible: Little or no market disruption when disease occurs on one or more farms
B. bronchiseptica is not a regulated or trade-restricting pathogen: (1) Not WOAH-listed: No international trade restrictions; (2) Ubiquitous globally: "worldwide distribution" and highly prevalent in swine populations everywhere; (3) Endemic status: Detection does not change herd health certification; (4) No public health trade implications: Rare human cases are not associated with pork consumption. The main economic impact is production losses rather than market access or trade restrictions. Slaughter plant findings (turbinate atrophy, pneumonia) affect individual carcass value but not herd or regional trade status.
PATHOGEN'S ABILITY TO DEVELOP AND SPREAD RESISTANCE
Level: Moderate risk: Evidence of development of clinically important resistance to antibacterial or antiviral treatments, or that development of such resistance is likely to occur over time
B. bronchiseptica shows variable antimicrobial resistance patterns with some concerning trends: (1) Intrinsic resistance: "Bordetella is largely resistant to beta-lactam antibiotics, including ampicillin and cephalosporins such as ceftiofur"; (2) Variable resistance reported: "Variable resistance has been reported to florfenicol"; "significant resistance to tilmicosin has been reported"; "some resistance to the tetracyclines has been reported"; "significant resistance of B. bronchiseptica to trimethoprim-sulfa combinations"; (3) Generally susceptible: Susceptible to enrofloxacin, tulathromycin, gentamicin, gamithromycin, tildipirosin; (4) Treatment limitations: "tylosin and tiamulin are ineffective against B. bronchiseptica." The combination of intrinsic beta-lactam resistance and acquired resistance to other classes creates moderate AMR concerns.
AMR DEVELOPMENT DRIVEN BY DISEASE MANAGEMENT
Level: High risk: Antibacterial or antiviral treatments commonly used on affected groups, or for prophylaxis
B. bronchiseptica management frequently involves population-level antimicrobial use: (1) PAR control programs: "The use of antibiotics to control cases of atrophic rhinitis includes administration by feeding or parenteral route to sows and piglets around the time of farrowing or weaning in an effort to limit the extent of colonization"; (2) Incomplete clearance drives repeated use: "Antibiotics may alleviate pneumonia and reduce clinical signs, but total clearance of Bordetella from the upper respiratory tract is difficult"; "B. bronchiseptica was not cleared from the nasal cavity, trachea, or lung after 7 days" of treatment; (3) PRDC involvement: As a PRDC component, B. bronchiseptica is often present during respiratory disease treatments involving multiple antimicrobials; (4) Carrier state persistence: Inability to clear infection leads to ongoing antimicrobial pressure in endemic herds.
AVAILABILITY OF EFFECTIVE TREATMENT OPTIONS
Level: Available but with uncertain efficacy: Limited treatments available in US or are only effective in some situations
Multiple antimicrobials are effective for clinical disease: (1) Labeled treatments: "Antibiotics labeled for the treatment of swine respiratory disease, and specifically B. bronchiseptica, include enrofloxacin, florfenicol, and tulathromycin"; (2) Additional effective options: "B. bronchiseptica appears susceptible to the newer macrolide antibiotics gamithromycin and tildipirosin"; also susceptible to gentamicin; (3) Treatment limitations: Beta-lactams ineffective; "ceftiofur is not the optimal choice when treating mixed infections that include B. bronchiseptica"; cannot achieve bacterial clearance—"nasal and tracheal colonization was only mildly reduced" even with treatment; (4) Disease reduction achieved: Treatment "reduced clinical and lesion scores" even without elimination; (5) Timing important: Early treatment more effective for limiting disease progression.
AVAILABILITY OF EFFECTIVE VACCINES OR BACTERINS
Level: Available but uncertain efficacy: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Multiple vaccine types are available with documented efficacy but important limitations: (1) Commercial products: "Vaccines for B. bronchiseptica largely consist of whole-cell bacterins, often in combination with P. multocida whole-cell bacterins or toxoids"; "a few attenuated intranasal vaccines available as well"; (2) Documented benefits: Vaccination "does significantly limit or even abolish clinical disease"; "Vaccination of sows around 6 weeks and again around 2 weeks prior to farrowing appears to work well to protect piglets"; piglet vaccination "can provide protection from turbinate atrophy"; (3) No sterilizing immunity: "Bacterins provide protection against disease manifestations such as turbinate atrophy but typically fail to protect animals from colonization. Thus, vaccinated animals can still serve as subclinical carriers"; (4) Pertactin importance: "Vaccines that elicit a response to pertactin...have been shown to be highly protective"; pertactin gene heterogeneity must be considered; (5) Maternal antibody interference: Can reduce piglet vaccine efficacy; (6) Intranasal vaccines: May provide superior mucosal immunity but results "have been mixed."
FEASIBILITY OF ERADICATING THE DISEASE FROM THE US
Level: Not feasible: Eradication extremely unlikely
B. bronchiseptica eradication is not achievable: (1) Ubiquitous prevalence: "worldwide distribution"; "highly prevalent among swine"; frequently isolated from healthy and diseased pigs; (2) Persistent colonization: "B. bronchiseptica persists in the nasal cavity for at least several months and perhaps indefinitely"; vaccination does not eliminate carriers; (3) Environmental survival: Remains viable up to 45 days in soil, weeks in water; (4) Multi-host pathogen: "infects poultry and a broad range of wild and domesticated mammalian species"; isolated from rodents, birds, raccoons, opossums near swine facilities; (5) Aerosol transmission: Cannot be fully prevented by biosecurity; (6) No clearance with treatment: "total clearance of Bordetella from the upper respiratory tract is difficult." The chapter notes uncertainty: "Whether or not B. bronchiseptica can be totally eliminated by these methods remains unclear." Control focuses on reducing clinical disease impact, particularly PAR, rather than elimination. Toxigenic P. multocida elimination is more achievable than B. bronchiseptica elimination.